Film Having a Liquid Absorbed Therein

ABSTRACT

The present invention relates to a film having a liquid at least partially absorbed therein, wherein the liquid has been applied to a surface of the film and prior to application of the liquid to the surface, the surface has been subjected to a surface activation treatment such that the surface has a surface energy of at least about 50 dynes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication Ser. No. 60/501,339, filed Sep. 8, 2003, and U.S.provisional patent application Ser. No. 60/454,444, filed 13 Mar. 2003.

FIELD OF THE INVENTION

The present invention relates to a film having a surface with a liquidat least partially absorbed therein. In particular, the presentinvention relates to a film for use as a packaging for a food productand especially relates to a tubular food casing for food, which is to becooked or otherwise heated within the casing.

BACKGROUND OF THE INVENTION

The present invention will be described with particular reference to afilm for use in packaging food. However, it will be appreciated that thefilm of the present invention may have applications and uses other thanin the food industry and no limitation is intended thereby.

There are a number of applications for articles having a material with aliquid absorbed onto a surface thereof. Such applications include“patches” as used for slow release topical administration of therapeuticagents and food casings for release of a flavouring and/or colouringagent into the food encased therein. However, the types of materialswhich can be used to form such articles are strictly limited to thosehaving suitable absorption or permeability properties for the desiredliquid.

In practice, this has severely restricted the types of materials whichmay be used. Generally for hydrophilic liquids, the materials used arecellulosic materials and derivatives or modifications of water solublepolymers such as polyacrylamide, polyvinyl alcohol, polyvinylpyrolidoneand the like. These materials are typically modified such that thearticles formed therefrom are no longer water soluble but are able toabsorb at least some water. The polymers may be crosslinked and/orblended or copolymerised with less hydrophilic and/or hydrophobicpolymers or monomers. A particular application of a film having a liquidabsorbed therein are cellulosic food casings having a smoke flavouringagent known as “liquid smoke” absorbed therein. Such casings have beendeveloped to be able to apply a smoke flavour and/or colour to a foodproduct as an alternative to the traditional smoking process.

The traditional smoking process involves stuffing a food to be smoked,such as a sausage, into a smoke permeable casing and hanging the stuffedfood product in a smoke house in which wood was burned at lowtemperature to generate smoke. Smoking by such traditional techniques islabour intensive, time consuming (with smoking times being up to anumber of days) and the level of smoke generated often conflicts withpollution laws.

In order to provide the benefits of a smoked product but without thedrawbacks of conventional smoking techniques, liquid smoke was developedsome 65 years ago. Liquid smoke is the aqueous condensate of naturalwood smoke, which contains aldehydes that react with proteins in themeat resulting in browning of the meat surface. This browning can givethe appearance of a naturally smoked product

Liquid smoke was originally sprayed onto meat products encased in porousnatural gut or cellulose casings prior to cooking by placing in an oven.The porosity of the casings allowed the liquid smoke to penetrate thecasing and into the meat. In practice, however, it has been found thatwith this spraying process it is difficult to provide a uniform coatingto the product. Further, the liquid smoke spray tended to run down thesides of the stuffed casing and gather at the lower end thereof. Thisuneven coating of liquid smoke resulted in a product having anundesirable blotchy appearance.

In the light of these difficulties, much work has been conducted with aview to providing a substantially uniform distribution of liquid smokeonto the surface. Some attempts have been made to incorporate liquidsmoke into the meat product itself. However, this provides either aninsufficient amount of agent on the surface to provide the desiredcolour, or imparts an excessively smoky flavour to the product.

A more successful approach has been to incorporate liquid smoke into acellulose casing or absorb liquid smoke onto the surface of a cellulosecasing. Techniques for absorbing liquid smoke onto a cellulose casinginclude dipping or spraying the cellulose casing with a liquid smokesolution so that the liquid smoke permeates to the interior surface foreventual transfer to an encased product. Such external treatment canpresent difficulties with further processing of the cellulose casingsand in particular, may interfere with shirring. Despite thesedifficulties, there are a number of liquid smoke treated cellulosecasings on the market.

The permeability and porosity of cellulose casings which on the onehand, makes them compatible for use with liquid smoke, on the other handintroduces serious and widely recognized disadvantages. First, celluloseproducts are highly permeable to water vapour. This allows moisture lossduring cooking and a corresponding decrease in overall weight of theproduct. This results in a reduced yield of product, which isdisadvantageous for commercial reasons. Further, cellulose casings arealso oxygen permeable which leads to spoiling and/or discolouration ofthe food product. As a result of this latter difficulty, food productscooked in cellulose casings must either by consumed shortly aftercooking, or be removed from the casings and wrapped a second time asquickly as possible after production with an oxygen impermeable barriercasing. This rewrapping step provides an opportunity for contaminationor infection of the food product that represents a loss in quality andshortening of shelf life. Further, the additional steps add to costs.

To address the disadvantages of permeable cellulose casings, water andoxygen impermeable thermoplastic casings were developed. When usingcasing of this type, there is negligible loss in weight during theproduction process or during storage and shipping. Further, the productcan remain sterile provided the casings remain intact. However, as aresult of the impermability of the casing, smoke in either gaseous orliquid form cannot penetrate the casing. Further, impregnation ofthermoplastic casings with liquid smoke or other colouring additives hasnot been successful since the plastics used cannot adequately absorb andstore impregnating agents. In order to impart a smoke colour to plasticencased products, it is necessary to remove the casings and apply smokeby techniques such as spraying or dipping liquid smoke or atomizing andthe product repackaged. These additional steps not only increase costbut increase the risk of contamination.

Another approach has been to provide a cellulose/plastic laminate, theinner cellulose layer having a coloring agent absorbed therein and theplastic intended to provide an oxygen barrier layer. In practicehowever, when meats are cooked in packages formed from this material,juices collect between the meat and package. Such a condition is knownas “cook-out” or purge . This is undesirable from a consumer acceptancepoint of view. Further, it has been observed that there is a tendencyfor flaking or chipping of the cooked meat surface during slicing.

There is a recognized need in the industry to provide a gas and moistureimpermeable casing having a food additive such as liquid smoke absorbedtherein. However, to date all attempts to solve this problem and providea commercially acceptable product have failed for one reason or another.One approach has been to blend a liquid smoke with a resin used for theinner layer of a plastic casing. This has been unsuccessful for a numberof reasons including reaction and volatilization of the liquid smoke atextrusion temperatures and delamination induced by the presence of theadditive.

Another approach has been to incorporate an absorbent additive into animpermeable plastic casing material. However, such a product has yet tobe adopted commercially and in tests conducted by the present inventoron one such material, have shown that there is still insufficientabsorption of liquid into the film and excess liquid remains on thesurface of the film.

If this excess liquid is not removed, the colour and flavour additivesdo not remain evenly dispersed on the film surface during subsequentprocessing such as shirring and stuffing. The result is non uniformtransfer of colour and flavour to the surface of the product.

If the excess liquid is removed by wiping, very little of the colour andflavour additives remain absorbed in the film structure and little or nocolour and flavour is transferred to the product surface.

If the casing is in the form of a flat sheet the excess liquid may beremoved by applying heat to dry off the moisture leaving the colour andflavour additives as a coating on the film surface. However, heating maybe difficult or not possible if the film is a heat shrink film. Thecasing can then be formed into a tube to encase the food product. Adelicate balance is required to have the coating adhere sufficiently tothe casing surface to withstand shirring and stuffing operations and yetrelease to the surface of the food product during processing.

If the casing is in the form of a tube, the liquid containing colour andflavour solution can be added to the inside of the tube by well knowntechniques known as slugging but there is no practical method to removethe excess liquid. Therefore sufficient flavour and colour cannot beadded without non-uniform transfer to the product surface.

It will be appreciated that in other applications unrelated to the foodindustry, it may also be desirable to provide an alternative to thosematerials currently used in applications where it is desirable to have aliquid at least partially absorbed therein. It is therefore an object ofthe present invention to provide a film having a liquid at leastpartially absorbed therein and a method for producing such a film thatmay at least partially overcome the above disadvantages, or provide thepublic with a useful or commercial choice.

DESCRIPTION OF THE INVENTION

In a first aspect of the present invention, there is provided a filmhaving a surface with a liquid at least partially absorbed therein,whereby prior to the liquid being applied to the surface, the surfacehas been subjected to a surface activation treatment such that thesurface has a surface activity of at least about 50 dynes.

The present invention relates to the surprising and unexpected discoverythat by subjecting a surface of a film to a surface activationtreatment, the surface may be coated with a layer of a liquid such thatthe liquid solution is at least partially absorbed into the film.

At least partially absorbed in to the surface is to be understood tomean that there is at least some impregnation of the liquid into thesurface as opposed to a coating which remains on the surface.

According to a further aspect of the present invention, there isprovided a method of preparing a film having a liquid at least partiallyabsorbed therein, the method including the steps of subjecting a surfaceof the film to a surface activation treatment such that the surface hasa surface energy of at least about 50 dynes, applying a liquid to thesurface such that the liquid is at least partially absorbed into thefilm.

The film of the present invention may be any suitable film for thedesired end use. Preferably, the film is for packaging a food product.More preferably, the film is a cook-in film. The film is formed from oneor more polymeric materials, present in one or more layers. Thepolymeric material may be any suitable material which may be processedas a film in either mono-layer or multi-layer configuration. Thepolymeric material may be a synthetic or non-synthetic polymer or amixture or blend thereof. Suitable materials for use in multi-layerfilms for food packaging applications include a food contact layer andone or more other layers selected from sealant layers, abuse layers,bulk layers, oxygen barrier layers, moisture barrier layers, tie layersand the like. The nature of these additional layers forms no part of thepresent invention. Those of ordinary skill in the art are aware ofsuitable polymers and blends thereof for use in the construction of foodpackaging films. Typical materials are known in the art and includepolyolefin materials such as low density polyethylene, linear lowdensity polyethylene, high density polyethylene, and higher alphaolefins such as polypropylene, polybutylene; ionomer resins, olefincopolymers with vinyl monomers such as ethylene vinyl acetate, ethyleneacrylic acid or blends thereof; polyvinyl chloride, polyvinylidenechloride, polystyrene and blends and/or copolymers thereof.

An especially preferred material for the surface activation treatment isa hydrophilic material such as a polyamide material. Suitable polyamidesare known in the food packaging art and include aliphatic polyamidessuch as homopolycondensates of aliphatic primary diamines having, inparticular, 4 to 8 carbon atoms and aliphatic dicarboxylic acids having,in particular, 4 to 10 carbon atoms and blends or mixtures thereof. Thealiphatic copolyamide may be the same homopolycondensate or homopolymer,and may be a polymer based on one or more aliphatic diamines and one ormore aliphatic dicarboxylic acids and/or one or moreomega-aminocarboxylic acids or omega-aminocarboxylic lactams. Examplesof suitable dicarboxylic acids include adipic acid, azelaic acid,sebacic acid and dodecane dicarboxylic acid. The film may also includean additive to facilitate adherence or absorption of the liquid.Suitable additives may include water soluble or water swellablematerials such as starches, celluloses including alpha cellulose, polyethylene oxides, poly vinyl alcohol, polycyclic acid, crosslinkedpolyvinylpyrrolidone (PVPP) and polyvinylpyrollidone (PVP) copolymers,mixtures and blends thereof. A preferred material is PVP or PVPP.

The surface of the film may also be treated to increase the surface areathereof. Such methods of surface treatment are known and includeablation and etching. Alternatively, the surface may be roughened duringextrusion by a number of methods including extruding through a rougheneddie, or setting the melt and die temperatures so as to create anon-uniform or turbulent flow. Alternatively, the polymer may be blendedwith additives that can promote melt fracture or modify flow. On theother hand, in some cases, processing aids are added to control meltfracture. The levels of these aids may be reduced or modified to givethe desired effect.

For some applications such as food packaging, the film is heatshrinkable such that it may conform tightly to the food product. Thefilm may be a cook-in film in which case it shrinks during cooking.Alternatively, the film may be shrunk prior to packaging the foodproduct by placing the package in a heated environment.

Typically, for food packaging purposes, the film is in the form of aseamless tubular casing. Such casings may be prepared by methods knownin the art. Alternately, the film may be formed as a single sheet,surface activated, coated and then formed into a tube by sealing theedges together. The process to form a single sheet into a tube bysealing is well known in the art and is known as back seaming. It isused on form and fill machines.

The surface activation treatment may be any suitable treatment methodsuch as plasma, flame, corona discharge, UV irradiation, electron beamirradiation, gamma irradiation and the like. The surface may also betreated chemically by subjecting the surface to oxidizing or etchingagents. A preferred treatment is corona discharge.

It is known to treat a polyolefin material by corona discharge so as toimprove the wettabilty of the surface so as to facilitate printing.Typically the polyolefin is treated to increase the surface energy fromabout 30-32 dynes up to about 37-40 dynes. The power levels required toprovide such increases in dyne level depend to some extent on the natureof the material to be treated and any additives therein. Differentmaterials may react differently. For example, polyesters are known torequire relatively low power levels of from about 8 to 11 W-m/M²,whereas polypropylene requires relatively “high” levels of about 22 toabout 27 W-m/M². Higher corona treatment levels are considered to beundesirable as it is believed there is a breakdown of the polymersurface and release of low molecular weight products which actuallyreduces the ability of the surface to bond to an ink or the like.

Treatment of a polyolefin layer that forms an interior surface of atubular food casing by corona discharge is also known. The purpose ofsuch treatment is to improve the meat adherence properties of thesurface. Typically polyethylene is treated such that the surface energyof the film is increased to between about 40 to 50 dynes. A certaindegree of adhesion to meat is desirable to avoid purge. However,excessive adhesion is also undesirable as the film does not releasecleanly from the meat surface and part of the meat is pulled away fromthe film. This results in a scarred and unsightly appearance. Excessiveadhesion is typically observed where the surface activity of the filmexceeds about 50 dynes. Corona treatment of the interior surface of atubular casing has been described in U.S. Pat. No. 5,296,170. Polyamidecasing materials which have a surface energy in the order of up to about45 dynes generally have sufficient meat adherent properties and coronatreatment is not required. It is believed that if a polyamide was coronatreated, the resulting film would adhere excessively to a meat surface,causing the above-mentioned problems.

Surprisingly it was discovered that when the corona treatment level wasincreased well above known commercial use, a liquid could be absorbedinto the film. Further where the film was a cook-in food packagingarticle, the film did not unduly adhere to the meat surface.

It will be appreciated that the level of surface treatment to which asurface is subjected will vary depending upon the nature of thesubstrate and the surface activation treatment and the amount of theliquid to be absorbed. The necessary level of treatment for a particularsubstrate may be determined by a person of skill in the art. Typically,the surface is treated so as to provide a coating absorbed level of atleast about 0.40 and up to about 10 mg/cm², preferably at least about1.0-3.0 mg/cm². Where the surface is treated by corona treatment, thesurface is typically treated at a Waft density of between about 50 toabout 1000 watt/min/m², most preferably from about 100 to about 600watt/min/m². The film may be treated with one or more sets of electrodesin series. The total watt density may be split as desired between theelectrodes.

The liquid may be any suitable liquid depending upon the desired enduse. It will be appreciated that the term liquid refers to any flowablematerial and includes pure liquids, aqueous or non-aqueous mixtures,suspensions, emulsions, solutions and compositions which may or may notcontain solids such as suspended particulate materials.

Typically, the liquid includes additives which may either modify theproperties of the film and/or be transferred to an article in contactwith the film. For example, in therapeutic applications, the additivemay be a therapeutic agent such as a drug, vitamin, conditioning agentor the like.

Where the film is for use in food packaging, the liquid typicallycomprises a colouring and/or flavouring agent with optional additivessuch as binders, gelling or thickening agents, surfactants and the like.Preferably, for cook-in purposes, the colouring agent is of the typethat reacts with proteins in food by the Maillard reaction, whichproduces a brown colour characteristic of smoked meat. The Maillardreaction may also imparts a smoky flavour to a food. Maillard reagentsmay be considered to be both a coloring and a flavoring agent. Compoundsthat react with proteins in this manner are active carbonyl compoundssuch as hydroxyacetaldehdye and reducing sugars such as fructose,glucose, ribose, lactose, xylose and the like. In the presentspecification, the general term “Maillard Reagent” will be used to referto any one or more of such compounds. Preferred Maillard type colouringagents are liquid smoke or colouring agents available under thetradename Maillose as available from Red Arrow. The Maillose agents areformed from pyrolysis of sugars and starches. Liquid smoke is acollection of condensable products from pyrolysis of wood or cellulose.Liquid smoke includes active carbonyl compounds with hydroxyacetaldehdyetypically being the major carbonyl product. Especially preferredcolouring agents are those that comprise a relatively concentratedamount of a Maillard reagent. Especially preferred is a colouring agentcomprising between about 20 wt % to about 40 wt %, most preferablybetween about 30 wt % to about 35 wt % hydroxyacetaldehyde.

Other colouring agents may be used instead of, or in addition to, theMaillose type colouring agents. Such further colouring agents are wellknown in the art and include caramel, beet extract, malt and bioxin.

Especially preferred compositions are currently under development by RedArrow. Such compositions include at least one viscosity modifying agent,a surfactant and a Maillard type coloring agent. Viscosity modifyingagents suitable for use in contact with food are well know in the artand include materials such as cellulose, methyl cellulose, hydroxypropylcellulose, starch, chitin, carrageenan, konjac, guar gum, xanthan,alginic acid and derivatives thereof, agar, pectin, gelatine and thelike. Preferred viscosity modifying agents are water-soluble celluloseethers such as, methylcellulose, hydroxypropyl methylcellulose,hydroxypropylcellulose, ethyl methylcellulose, hydroxyethylcellulose,ethyl hydroxyethylcellulose and preferably the anionic water-solublecellulose ethers such as, carboxymethylcellulose and carboxymethylhydroxyethylcellulose. Mixtures of water-soluble cellulose ethers mayalso be employed. Particularly preferred cellulose ethers are the methylcellulose ethers under the trade name Methocel. Typically, thecomposition includes up to about 2.0 wt %, preferably up to about 1.0 wt% of a viscosity modifying agent.

A preferred composition includes between about 0.05 to about 0.5%, mostpreferably between about 0.125 and 0.25 wt % of a viscosity modifyingagent.

Typically, the composition includes one or more surfactants. Suitablesurfactants include calcium stearoyl lactylate, diglycerides, dioctylsodium slilfosuccinate, hydroxypropyl cellulose, lecithin,monoglycerides, polysorbate 60, 65, and 80, a glycol such as propyleneglycol, sodium hexametaphosphate, sodium lauryl sulfate, sodium stearoyllactylate, sorbitan monostearate, or mixtures thereof.

An especially preferred composition includes a Maillard type colouringagent in combination with a methylcellulose and a glycol such aspropylene glycol, preferably up to about 10 wt %, more preferably up toabout 5 wt % glycol.

The composition may also include optionally other additives such asanti-oxidants and stabilizers.

It will be appreciated that the type of and amount of the components ofthe liquid composition may be selected according to the nature of thesurface and also the food to be packaged therein. Consideration may begiven to a desirable colour or flavour profile of different meatproducts with a view to consumer acceptance.

Alternatively, or in addition to the colouring or flavouring agents, theliquid may also include an antimicrobial agent, an antibacterial agent,a fungicide and/or an antiviral agent. It will be appreciated thatincorporation of such agents need not be limited to use in foodpackaging and may have other applications.

The liquid may also consist essentially of water. The present inventorhas surprisingly observed that when films which are typically quitestiff are treated according to the method of the present invention, theamount of water which may be absorbed is sufficient to alter thephysical properties of the film such that the film is soft and pliable.An application of a softer film is in the food packaging industry wherefood products are stuffed into a tubular casing prior to being placed ina metal mould, which is typically of a square or rectangular crosssection. Foods packaged and cooked in this way are referred to asmoulded products. The flexibility of the film allows the film to conformto the shape of the mould. On the other hand, for some applications suchas stuffing (where a food product is injected into a tubular casing andcooked to provide a product of circular cross section) a film havingless flexibility may be desired.

The degree of flexibility may be controlled or modified by controllingthe amount of liquid absorbed and/or formulating the film to provide atleast two layers, a first layer into which the liquid is to be absorbedand a second water impermeable or barrier layer. It will be appreciatedthat such films may also include other layers. An example of such anarrangement is a film for use as a food packaging film having an innerlayer of a hydrophilic material such as a polyamide material and a layerof a polyolefin material such as polypropylene, polyethylene or LLDPE.

The liquid may be applied to the surface by any suitable technique suchas soaking or spraying. A suitable process for tubular casings is knownin the art as slugging. Slugging is described in U.S. Pat. No. 3,378,379and is used to apply a coating to absorbent cellulose casings. Theconventional slugging method for coating the inside of a casing involvesfilling a portion of the casing with the coating material, so that a“slug” of material generally resides at the bottom of a “U” shape formedby the casing and then moving a continuous indefinite length of casingso that the slug of coating material remains confined within the casing,while the casing moves past the slug and is coated on its inside wall bythe coating material contained within the slug. The film then passesbetween a pair of cog rollers.

Preferably, a modified slugging process is used to apply the liquid tothe surface in which the slug is trapped between an upper and lower pairof nip rolls. The upper set of rolls preferably includes a chrome platedroller and a rubber roller. The rubber roller typically has a hardnessof between about 60 to about 120, typically between about 70 to about100 durometer. As the tube passes between the two sets of rolls, liquidis carried with the tube and the upper set of rolls act as meteringrolls. In the embodiment of the invention, where the liquid consistsessentially of water, it is preferred that the water include a viscosityincreasing agent. Increasing the viscosity facilitates passage of theliquid towards the upper set of rolls.

Preferably the gap between the roller is set at less than the thicknessof the tube, typically at about 50%. This is in contrast to conventionalcoating techniques where the gap is set equal to the tube thickness plusthe desired thickness of the coating layer. Whilst not wishing to bebound by theory, it is believed that the pressure created as the tubepasses between the rollers assists in forcing the liquid into the wallsof the film. Typical levels of absorption are in the order of 20 to 35%by weight.

Food casings composed of the film of the present invention may beprovided in any of the forms known in the art, such as in the form ofshirred casing sticks, discrete short segments of flattened casings,continuous lengths of flattened casing on a reel and the like.

Where the film is in the form of a tubular casing, the tube is typicallyshirred after application of the liquid. Shirring may be accomplished byconventional shirring techniques as well known to those of skill in theart.

According to a further aspect of the invention, there is provided ashirred tubular food casing having an inner food contact surface coatedwith a liquid composition comprising at least one food additive fortransfer to a food product encased therein, whereby prior to applicationof the composition to the surface, the surface has been subjected to asurface activation treatment.

After application of the liquid, the film may be used to package a foodproduct by any suitable means. Where the package is in the form of atubular casing or a shirred casing, the casing may be stuffed by pushinga meat product through a stuffing horn into the inside of the tubularcasing.

A food product packaged within the film of the invention may be cookedby any suitable method such as boiling, heated by steam, or placed in anoven. Preferably, the packaged food is cooked as soon as possible afterpackaging. Alternatively, the packaged food product may be subjected toa pre-heating step so as to fix the colour prior to cooking. Forexample, the packaged product may be pre-heated to a temperature ofbetween about 150° F. and about 200° F. for a period of up to about 6minutes. During cooking, the food colouring additive can impart a colourto the surface of the food.

According to a further form of the invention, there is provided a methodof processing a food product, the method including packaging the foodproduct within a film of the first aspect of the invention whichincludes a colouring agent and heating the packaged article to atemperature at which colour from the colouring agent is transferred tothe surface of the food product.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a photograph of a ham packaged in a film of the inventionas compared to a control ham;

FIG. 2 shows a photograph of a turkey product packaged in a film of theinvention as compared to a control turkey;

FIG. 3 shows a SEM of a film designated DC-1 AD-1;

FIG. 4 shows a SEM of the film of FIG. 3 impregnated with a colouringcomposition, FIG. 5 shows a SEM of the film of FIG. 3 after methanolextraction; and

FIG. 6 is an SEM of the film of FIG. 4 after methanol extraction.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1 Coating Formulations

Coating formulations were prepared by Red Arrow according to Table 1.

TABLE 1 Coating Coating Composition Code component wt % C/C_(3/02)/Maillose 45 _(1.) 94.63 C_(1/03) Propylene Glycol 5.00 DioctylSulfosuccinate 0.25 Xanthan Gum 0.12 C_(x) Liquid smoke _(3.) 100.0 C₇Maillose 45 94.875 Propylene Glycol 5.00 Methocel ^(2.) SGA16M 0.125 C₉Liquid smoke 94.875 Propylene Glycol 5.00 Methocel SGA16M 0.125 C₂₀Maillose45 98.4 Propylene Glycol 1.4 Methocel K 100M 0.2 C₂₁ Liquidsmoke 98.4 Propylene Glycol 1.4 Methocel K 100M 0.2 _(1.) Maillose 45contains 27 wt % hydroxy acetaldehyde, is a colourant available fromArrow Products Co. LLC, Manitowoc, WI and formed by the pyrolysis ofsugars. ^(2.) Methocel is methyl cellulose available from Dow. _(3.)Liquid Smoke is a concentrated liquid smoke product having hydroxyacetaldehyde content of between about 30 to about 35 wt % and isavailable from Red Arrow Products Co. LLC, Manitowoc, WI.

EXAMPLE 2 Corona Treatment of a Polyamide Film

The following trials were conducted with a three layer heat shrinkabletubular film having an outer polyamide layer, an intermediatepolypropylene copolymer layer and an inner polyamide layer. The innerlayer is a blend of nylon 6 and about 16% PVPP. This film will bereferred to hereinafter as DC-1.

The tubular film was internally corona treated at 600 W using anelectrode arrangement similar to that as described in U.S. Pat. No.5,296,170 in which one of a pair of electrodes is placed in contact withone side of an inflated tube. In this way, a corona discharge isgenerated in the air space within the tube. However, a significantdifference between the method as described in U.S. Pat. No. 5,296,170 isthat in the present case, much higher power levels are used. AlthoughU.S. Pat. No. 5,296,170 does not describe the power level in wattdensity, the examples show an increase in dyne level of a polyethylenefilm from 31 dyne to 42 and 41 dyne. However, it may be estimated fromthis change in dyne level that a power of between about 18 and 23 wattwas used. After corona treatment, the interior surface of the film wascoated by slugging as described below:

1. The tube is slit open and an amount or “slug” of the liquid is added.

2. Air is injected to form the tube into a cylindrical shape and theslit is sealed with a tape.

3. The tube is advanced through and partially collapsed through a set ofcoating rolls. The rolls include a 72 durometer rubber roll and a chromeplated roll. The spacing between the coating rolls is adjustable suchthat the rolls are not totally closed and the gap is about 50% of thetube width. As the film with the liquid passes through the rolls, mostof the liquid is squeezed out.

4. The film with the film absorbed on the inside surface is then woundinto reels.

The level of surface activation was estimated by measuring the surfaceenergy in dynes. The results are summarized in Table 2.

TABLE 2 Corona Dyne Watt- Add-on* Delta Add-on Treatment level min/m2Mg/cm² mg/cm2 Increase % None 52  0 0.40 0 0 Yes 55** ca76 0.46 0.06 15Yes 66-70 228 0.67 0.27 67.5 *The amount of coating retained wasmeasured by weighing the film before and after coating. **A film treatedto this level is referred to as DC1-AD1 hereafter. This film had beencorona treated by a conventional corona treater used to treat tubularcasings (as described in U.S. Pat. No. 5296170) to the maximum poweravailable. It is estimated from the measured dyne level that the wattdensity was in the order of 75 Watt-min/M².

The coating used was Coating C1, the components of which are provided inTable 1.

The results in Table 2 show a 67% increase in the amount of solutionthat can be absorbed into the inner layer. and that the amount ofcoating that can be absorbed into the inner surface of the film wasdirectly related to the level of corona treatment.

In the experiments it was observed that the surface activation was sohigh, that the dyne level was outside of the usual dyne measurementtechniques. For this reason in future tests the level of surfaceactivation was estimated in terms of watt density.

Waft density is calculated according to the following formula:

${{Watt}\mspace{14mu} {density}} = \frac{{power}\mspace{14mu} {supply}\mspace{14mu} ({watts})}{{Width}\mspace{14mu} {of}\mspace{14mu} {{tube}(M)} \times {line}\mspace{14mu} {speed}\mspace{14mu} \left( {\min \text{/}M} \right)}$

It may also be appreciated by a person of skill in the art that theabove dyne levels are well in excess of that achieved by coronatreatment as used to facilitate meat adhesion. It is generally acceptedthat level of between 40 to 50 dynes provide acceptable meat adhesion.It is also generally accepted in the field that if films are treated toa dyne level above about 50 dyne that the film unduly adheres to themeat surface. In the present instance it was surprisingly observed thatdespite these high levels of surface activation and contrary toexpectations the meat film released cleanly from the meat surfacewithout meat scarring.

To further demonstrate that the amount of liquid that can be absorbedinto a polyamide film is a function of the corona treatment the filmused in the tests of table 1 was treated to two different corona levels.Moisture was then applied to the film and the amount of moistureabsorbed was determined per ASTM 570. This test requires specimens to beconditioned in an oven for 24 hours at 50° C. cooled in a desiccator,then immediately weighed to the nearest 0.001 g. After conditioning, thetest specimens were immersed in distilled water that was maintained atroom temperature (23+−1 C) for 72 hours. After the end of the test, thespecimens were removed from the water, all surface water was wiped offwith a dry cloth, and then weighed immediately to the nearest 0.0001 g.

To calculate the percentage increase in weight during immersion, thefollowing equation was used:

${{Increase}\mspace{14mu} {in}\mspace{14mu} {weight}},{\% = {\frac{\left( {{{Wet}\mspace{14mu} {weight}} - {{Initial}\mspace{14mu} {weight}}} \right)}{{Initial}\mspace{14mu} {weight}} \times 100}}$

Table 3 show the results of the test.

TABLE 3 Test Casing Type % Weight Gain W-m/M² 1 DC-1 (no corona) 12.9 —2 DC1-AD-1 14.7 About 75 3*** DC1-AD-1 18.7 189.3 ***For test 3 the filmof DC1-AD-1 the inner surface was further treated to the levelindicated. It is estimated that the dyne level is 70 or higher at thewatt density indicated but at these levels the dyne test cannot be usedwith any reliability.

results indicate that corona treatment increases the amount of moisturethat is absorbed as the corona level is increased.

To demonstrate that a solution that contains smoke colour is alsoabsorbed when applied to the inner surface of the film the followingtest was devised:

Film samples were cut to fit circular hoops similar to those used tohold cloth when doing needle point. The inner surface of the film wasplaced in the hoop so that the rim of the hoop and the film formed acontainer. Before the film was clamped into the hoop.

The film specimens were clamped into the hoops. A solution that containsMaillose (C20) was added to the inner surface of a film of the structurepolyamideltie/polyamide. (This film will be referred to hereinafter asV9). The solution was added to just cover the surface of the film. Thismethod insures that only the inner surface of the film has solutionapplied and closer simulates the slugging process. The specimen was leftin contact with the solution for 72 hours.

The excess solution was poured from the hoop, the specimens were removedfrom the hoop and, all surface solution was wiped off with a dry cloth.The specimens were heated to 250 F for 30 minutes and then weighed tothe nearest 0.0001 g.

Table 4 summarizes the results obtained for this test.

TABLE 4 Material Treatmentw-min/m2 Absorption % V9-control 0 23.9% V9-5050 28.6% V9-100 100 30.4% V9-150 150 37.0% V9-200 200 33.1% V9-250 25032.2% V9-300 300 30.6% V9-400 400 30.1% V9-500 500 31.4%

The results indicate that as the internal coronal level was increasedthe amount of solution that was absorbed also increased.

EXAMPLE 3 Shirring Stuffing and Processing

Films were activated and compositions applied thereto in a manner asdescribed in Example 2. The films, after allowing time for the coatingto attach and/or be absorbed onto the rolls were shirred into “sticks”.Shirred tubular casings may be prepared by conventional shirringmachines as known in the art.

Ham or turkey meat products were then pushed through a stuffing horninto the shirred casings.

The encased food products were then cooked by heating in an oven, withsteam or hot water set for a length of time for the product to reach aninternal temperature of 160 F. The oven was maintained at 100% relativehumidity and a temperature of 185 F. The steam and hot watertemperatures are noted in Table 3. Cooking was conducted as soon aspracticable and at various times after stuffing as noted.

Controls were conducted in the absence of corona treatment andimpregnation.

The results are summarized in Table 5.

TABLE 5 Product Composition Treatment Add On % increase in ColorimetricType Code Colourant Film Type Inner Layer W-M/m2 mg/cm2 weight of film*L Value Comments Bologna C₂₀ Maillose DC-1 AD-1 Nylon + PVPP 318 0.6726.35 53.21 Uniform dry golden mahogany Bologna C₂₁ Liquid Smoke DC-1AD-1 Nylon + PVPP 309 0.76 29.99 54.48 Uniform dry golden brown BolognaNone None DC-1 AD-1 Nylon + PVPP None 0 0 65.57 Uniform dry pale tan.Ham C₉ Liquid Smoke DC-1 AD-1 Nylon + PVPP 102.6 1 39.33 56.62 Moulded165° F. Water Ham C₉ Liquid Smoke DC-1 AD-1 Nylon + PVPP 102.6 1 39.3353.18 Moulded 195° F. Water Ham None None V-1 Control LLDPE None 0 065.13 Moulded 165° F. Water Turkey C_(3/02) Maillose DC1 AD-1 Nylon +PVPP 300 0.42 16.62 67.4 Uniform, light colour Turkey None None V-1Control LLDPE None 0 0 75.1 Uniform, light colour Turkey C₇ Maillose DC1AD-1 Nylon + PVPP 216.2 0.84 33.04 61.56 Processed immediately 185°Steam Turkey C₇ Maillose DC1 AD1 Nylon + PVPP 216.2 0.84 33.04 69.78Held 4 hours 185° Steam Turkey C_(1/03) Maillose DC1 AD1 Nylon + PVPP289 0.82 33.04 67.99 1 Minute Hot Water Held 4 hours 185° Steam TurkeyC_(1/03) Maillose DC1 AD1 Nylon + PVPP 289 0.82 33.04 62.3 3 Minute HotWater Held 4 hours 185° Steam Turkey C_(1/03) Maillose DC1 AD1 Nylon +PVPP 289 0.82 61.8 6 Minute Hot Water Held 4 hours 185° Steam TurkeyNone None V-1 Control LLDPE None 0 0 75.47 Turkey Cx Liquid smoke DC1AD1 Nylon + PVPP 256 1.4 64.19 Turkey C9 Liquid Smoke DC-1 AD-1 Nylon +PVPP 102.6 1 39.33 65.6 Moulded 165° F. Water Turkey C9 Liquid SmokeDC-1 AD-1 Nylon + PVPP 102.6 1 39.33 63.38 Moulded 195° F. Water TurkeyNone None V-1 Control LLDPE None 0 0 75.94 Moulded 165° F. Water Ham C9Liquid smoke V-1 control LLDPE  0 0 0 64.99 Ham C9 Liquid smoke VisflexNylon 616.0 0.85 57.61 Ham C9 Liquid Smoke V9-2 Nylon 616.0 0.80 56.37Ham C9 Liquid Smoke AD-1 Nylon + PVP 200.00 0.80 31.36 55.89 Ham Sunproducts Absorbent None None 52.79 Moulded Fibrous 165F. cellulose waterHam C9 Liquid Smoke AD-2 Nylon 308 0.93 51.40 L value-The lower thenumber, the greater the Colour density *The % weight increase of thefilm was calculated from the add on according to the formula:${\% \mspace{14mu} {weight}{\mspace{11mu} \;}{increase}} = \frac{{{add}\mspace{14mu} {on}\; \times 100}\mspace{14mu}}{{wt}\mspace{14mu} 1{{cm}^{2}\left( {2.5423\mspace{14mu} {mg}} \right)}}$

Visflex is a commercially available film from Viskase and has thestructure: nylon/EVA/nylon.

V9-2 is a commercially available film from Vector and has the structure:nylon/tie/nylon.

V1 is a commercially available film from Vector and has the structure:nylon/tie/LLDPE.

Sun Products is a commercially available absorbent plastic/celluloselaminate casing having a colorant solution absorbed therein.

It was discovered that the final colour transferred to the product isaffected by the time between stuffing and processing. It is believedthat this is because the heat of processing sets the colour on theproduct surface. If held before processing the colour compounds areabsorbed into the meat product.

It was also observed that when the process was run without surfacetreatment that excessive pooling occurred above the upper coating rollsand liquid collected at low points of the tube. Further, the coatedsurface was wet to the touch and it was possible to wipe liquid from thesurface. Although there was some add on and some color was transferredto the meat product, in practice the color transfer was streaky andquiet unacceptable indicating a non-uniform coating onto the surface.This non-uniform coating was insufficiently absorbed so as to beresistant to the subsequent shirring and stuffing operations. On theother hand, when the tube was corona treated, no pooling was observed.Also the inner surface of the tube did not feel wet, nor was it possibleto wipe off any liquid from the treated surface. It is believed thatthese observations support the belief that the liquid is at leastpartially absorbed into the surface and not present as a discretecoating.

FIG. 1 shows a photograph of a ham packaged in a film of the inventionas compared to a control ham.

FIG. 2 shows a photograph of a turkey product packaged in a film of theinvention as compared to a control turkey.

These figures show that both the ham and turkey products cooked in thefilm of the invention have a uniform smoked brown colour. Uniformity ofcolour indicates that the composition can not only be uniformly absorbedinto the surface but this uniformity is resistant to disruption by theshirring and stuffing procedures. The absorbed liquid also has exhibitedthe flexibility to stretch during stuffing and shrink during heatshrinkage of the film. Still further, there is no evidence of purge, orcook-out, or an unacceptable adherence of the film to the meat product.

EXAMPLE 4 SEM Studies

In order to further investigate the absorption characteristics of atreated film scanning electron microscope studies were conducted on DC1,and DC1-AD-1 which had been treated to a power level of about 300W-min/M² and composition C7 applied to the treated surface. Initialresults showed that the principal difference between untreated andabsorbed film was that a 10 micron thick porous inner layer withirregular surface morphology was changed into a 5 micron thick porouslayer and a 5 micron thick nonporous innermost layer with irregularsurface morphology. This indicated that the composition had absorbedinto the inner film layer and impregnated the inner layer to a depth ofabout Y2 the original thickness.

To confirm this, further SEM analysis was conducted on water andmethanol extracted DC-1 AD-1 before and after liquid application to theinner surface. The results of the water and methanol extractedimpregnated samples showed that extraction with water and methanol leftphysical demarcations on morphologies of impregnated film layers atapproximately half the depth of their original cross sectionalthickness. Exemplary SEM micrographs taken at 1000× magnification areshown in FIGS. 3,4,5 and 6 which show unimpregnated, impregnated,methanol extracted unimpregnated and methanol extracted impregnatedfilms respectively.

It can be seen that the film and method described above, can provide afilm saving a significant amount of a liquid absorbed therein. Thetubular casing of the preferred embodiment is able to have a liquidapplied evenly thereto. Further the tubular casing is able to undergoshirring, stuffing and cooking operations so as to provide an eventransfer of additive to a food surface.

It will be appreciated that various changes and modifications may bemade to the invention described herein without departing from the spiritand scope thereof.

1. (canceled)
 2. The method of claim 18 wherein the surface activationtreatment is selected from the group consisting of plasma treatment,flame treatment, corona discharge, UV irradiation, electron beamirradiation, and gamma irradiation.
 3. (canceled)
 4. (canceled) 5.(canceled)
 6. The method of claim 18 wherein the liquid has been appliedto the surface in an amount of between about 0.4 to about 10 mg/cm². 7.(canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled)
 11. (canceled) 12.(canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)
 16. (canceled)17. (canceled)
 18. A method of preparing a nylon film having a liquid atleast partially absorbed therein comprising subjecting a surface of thenylon film to a surface activation treatment such that the surface has asurface energy of at least about 70 dynes, then applying a liquid to thesurface such that the liquid is at least partially absorbed into thefilm, wherein an amount of liquid able to be absorbed by the nylon filmafter said surface activation is greater than an amount of liquid ableto be absorbed before said activation.
 19. The method of claim 18,wherein the surface activation treatment is corona discharge.
 20. Themethod of claim 19, wherein the corona discharge has been conducted at apower level of between about 50 and 1000 W-m/M².
 21. The method of claim20, wherein the power level is between about 100 to about 600 W-m/M².22. The method of claim 18, wherein the film is in the form of a foodpackaging film, whereby in use the surface is an inner surface of thefilm.
 23. (canceled)
 24. The method of claim 18, wherein the nylon filmcomprises a nylon and a crosslinked polyvinylpyrrolidone.
 25. The methodof claim 24 wherein the film is a monolayer.
 26. The method of claim 22wherein the food packaging film has at least two layers, a first layercomprising the a nylon and an optional crosslinked polyvinylpyrrolidone,and a second layer comprising a layer of a polyolefin material, wherebyin use, the first nylon layer is an inner layer and the secondpolyolefin layer is an outer layer thereof.
 27. The method of claim 22,wherein the film is in the form of a tubular casing.
 28. The method ofclaim 27, wherein after the liquid is applied to the surface, the casingis shirred.
 29. The method of claim 22 wherein the liquid consistsessentially of water.
 30. The method of claim 22, wherein the liquid isa composition comprising at least one additive for transfer to apackaged food article packaged in the food packaging film.
 31. Themethod of claim 30, wherein the additive is selected from the groupconsisting of a coloring agent, a flavoring agent, and a coloring andflavoring agent.
 32. The method of claim 30, wherein the additivecomprises a Maillard reagent.
 33. The method of claim 18, wherein afterthe liquid has been applied to the surface, the film is passed between apair of nip rolls and a spacing between the nip rolls is set at adistance less than the thickness of the film.
 34. (canceled) 35.(canceled)
 36. (canceled)
 37. (canceled)
 38. (canceled)
 39. (canceled)40. (canceled)
 41. (canceled)
 42. The method of claim 18 wherein thenylon film consists of (a)(i) one or more aliphatic primary diamine andone or more aliphatic dicarboxylic acid, (ii) an omega-aminocarboxylicacid, (iii) an omega-aminocarboxylic lactam, or (iv) a mixture of two orthree of (i), (ii), and (iii), and optionally, (b) a crosslinkedpolyvinylpyrrolidone.
 43. The method of claim 18 wherein the nylon isnylon
 6. 44. The method of claim 26 wherein the food packaging film hasa third nylon layer over the polyolefin layer.
 45. The method of claim44 wherein the third layer comprises nylon
 66. 46. The method of claim18, wherein the liquid is absorbed to a depth of up to about one-half ofa thickness of the nylon surface layer.
 47. The method of claim 18,wherein the liquid is absorbed to a depth of up to about 5 microns of athickness of the nylon surface layer.
 48. The method of claim 18,wherein the surface of the film receives energy of a watt density of atleast 50 W-min/m².
 49. A method of preparing a nylon film having aliquid at least partially absorbed therein comprising subjecting asurface of the nylon film to a surface activation treatment by anapplication of energy such that the surface receives energy of a wattdensity of at least about 75 W-min/m², then applying a liquid to thesurface such that the liquid is at least partially absorbed into thefilm, wherein an amount of liquid able to be absorbed by the nylon filmafter said surface activation is greater than an amount of liquid ableto be absorbed before said activation.
 50. The method of claim 49,wherein the surface of the nylon film receives energy of a watt densityof up to about 500 W-min/m².
 51. The method of claim 49, wherein theliquid is absorbed up to about one-half of a thickness of the nylonfilm.
 52. The method of claim 49, wherein the liquid is absorbed to adepth of up to about 5 microns of a thickness of the nylon surfacelayer.
 53. The method of claim 49, wherein the liquid has been appliedto the surface, the film is passed between a pair of nip rolls and aspacing between the nip rolls is set at a distance less than thethickness of the film.